Manufacture of paper pulp



A. M. THOMSEN MANUFACTURE oF PAPER PULP Filed Aug. 1, 1927 ifi 85052@NVENTOR.

May 13, 1930.

Patented May 13, 19.30

UNITED 'STATES ALFRED M. THOMSEN, F SAN FRANCISCO, CALIFORNIA.

MANUFACTURE OF PAPER PULP Application led August 1, 1927. Serial No.209,791.

This invention'relates to improvements in the manufacture of paper pulp;the improvements which I have eected deal in a general way with the useof alkali sulphides i such as sodium sulphide, potassium sulphide or amixture of both as a cooking liquor.

As used to-day in the processes known by the names of sulphate andkraft, sodium sulphide is used in conjunction with caustic soda as themeans of liberating they cellulose fiber from the en'crusting materials.It is generally7 held that the principal agent in the progressivehydrolysis, destruction and solution of the encrusting substances is thecaustic soda and that the sulphide only comes into play close to the endwhen the caustic soda is almost or entirely spent.

The present system of recovery includes evaporation, incineration,smelting, leaching and causticizing. This produces a peculiar mixture ofsulphate, carbonate, hydrate and sulphide of soda, the cooking liquorbefore referred to, which gives the special results wanted in thesulphate and kraft processes. The loss ofsoda is made up by the additionof sodium sulphate.

ln my process I relyentirely upon sodium or potassium sulphide todissolve the encrusting substances which necessitates n radically newmethod for the regeneration of the alkali salts employed; in my processl employ in place of this series of operations,

evaporation to a syrupy consistency, absorption in charcoal orbriquetting with chain coal, destructive distillation with recovery ofthe volatile products, leaching of the resulting charcoal for therecovery ot the alkali salts, and separation of the alkali carbonateproduced in the process so as to preserve a strong sulphide solution.The loss of alkali is made up by the addition of sulphide.

The ber produced bly this process is very hard to bleach with chlorine4or its derivatives, but it may beeasily bleached by means ofpermanganate or more cheaply by means of a solution of alkali manganatewith or without the aid of CO2. y process is therefore, best consideredunder three aspects,

v namely, (a) the cooking of the pulp, (b) the regeneration of thecooking liquor, (o) and the bleaching of the ber.

The several steps of the invention are shown in the accompanying drawingwhich illustrates a diagrammatic flow sheet of the process.

(a) Ooolcz'ngf-The solvent action of strong solutions of sulphide uponthe encrusting matters is so much greater than upon the liber that veryvarying'woods or mixtures of woods and barks, or such materials asbamboo, grass, straw, sugar cane bagasse, cornstalks, etc., are readilyresolved into pulp. It is not necessary to cook under pressure, as asuiciently strong solution will do the work just as well underatmospheric conditions. l can, therefore, employ simple tanks withfilter bottoms, with er Without circulation of the cooking liquor, suchas are generally used in cooking es arto. However, if weaker solutionsare esired, tanks which permit cooking under pressure may be employed. l

(In) Regeneration-When a cook is finished, the pulp is washed 'free fromliquor, and both cooking liquor and wash water evaporated to theconsistency of syrup. This is now mixed with sucient charcoal to stiftenit. It may be either briquetted or put in shallow trays,\placed onproper metal cars and run into an oven as if it were cord wood. By meansof heat the organic combinations with alkali are resolved into charcoal,volatile substances, and alkali salts. rlhe volatile products arerecovered, refined and marketed. The charcoal and alkali salts areseparated by leaching out the alkali, which is resent partly ascarbonate, partly as sul hi e. As the former is the less soluble salt,1t is removable, partially at least, by fractional crystallization, andso prevented from accumulating to an undue extent. The loss of alkali ismade up by the addition of sulphide. The charcoal is used in part tofstien a succeeding charge, the rest is burnt, or marketed.

- (c Bleaching-nas reduced by this process t e ber is of, a b ackishgray to brown color, very stron and free from incrusting matter. Asstate p before,.it is very hard to bleach it with chlorine or itsderivatives but it yields easily to permanganate. l have found alkalimanganates equally efficient. It

` is easily prepared by fusing manganese ore With caustic alkali,dissolving the melt in Water and using the resulting green solution inplace of permanganate. If CO2 or Washed chimney gases be blown throughsimultaneously, the action is expedited. The spent liquor may beseparated from the pulp, brought up to strength with fresh manganate andre-used. After a number of such repetitions it Will become so strong inalkali that same may be profitably extracted. The pulp is subsequentlycleaned by means of sulphur dioxide in the customary manner. Here, also,the process may be rendered cyclic andthe dissolved manganese ultimatelyprecipitated and recovered.

Having thus described my invention, what I claim and desire to secure byLetters Patent is l. A process for liberating fiber obtained from avegetable source from encrusting materials which consists in cooking theiber in a solution of alkali sulphide only, Washing the ber, bleachingthe liber by subjecting it to a solution of alkali manganate, andsimultaneously passing carbon dioxide gas through the solution.

2. A process for liberating ber obtained from a vegetable source fromencrusting materials which consists in cooking the fiber in a solutionof alkali sul hide only, Washing the ber, bleaching the fEi'ber bysubjecting it to a solution of alkali manganate, and then cleaning thefiber by subjecting it to the action of sulphur dioxide.

3. A process for liberating ber obtained from a vegetable source fromencrustingmaterials Which consists in cooking the fiber in a solution ofalkali sul hide only, Washing the ber, bleaching the gber by subjectingit to a solution of alkali manganate, simultaneously passing carbondioxide as through the solution, and then cleaning t e liber bysubjecting it to the action of sulphur dioxide. ALFRED M. THOMSEN.

